Fuel cell

ABSTRACT

A fuel cell includes a cathode side separator. An oxygen-containing gas flow field is formed on a surface of the cathode side separator. The oxygen-containing gas flow field includes an inlet channel having a plurality of flow grooves connected to the oxygen-containing gas supply passage, an outlet channel having a plurality of flow grooves connected to the oxygen-containing gas discharge passage, and an intermediate channel having flow grooves with both ends connected to the inlet channel and the outlet channel respectively. The flow grooves of the outlet channel are longer than the flow grooves of the inlet channel, and the flow grooves of the outlet channel are narrowed toward the oxygen-containing gas discharge passage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No. 12/726,751, filed Mar. 18, 2010, which is based upon and claims the benefit of priority from Japanese Patent Applications No. 2009-066702 filed on Mar. 18, 2009 and No. 2009-109065 filed on Apr. 28, 2009, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell formed by stacking an electrolyte electrode assembly and a separator in a stacking direction. The electrolyte electrode assembly includes electrodes and an electrolyte interposed between the electrodes. A reactant gas supply passage and a reactant gas discharge passage extend through the fuel cell for allowing a reactant gas to flow in the stacking direction. A reactant gas flow field is formed between the electrolyte electrode assembly and the separator for allowing the reactant gas to flow along an electrode surface.

2. Description of the Related Art

The fuel cell is a system for obtaining direct current electrical energy by supplying a fuel gas (gas chiefly containing hydrogen) to an anode and supplying an oxygen-containing gas (gas chiefly containing oxygen) to a cathode for inducing electrochemical reactions at the anode and the cathode.

For example, a solid polymer electrolyte fuel cell includes a power generation cell formed by sandwiching a membrane electrode assembly between separators. The membrane electrode assembly includes an anode, a cathode, and an electrolyte membrane interposed between the anode and the cathode. The electrolyte membrane is a polymer ion exchange membrane. In use of this type of power generation cell, typically, predetermined numbers of the membrane electrode assemblies and the separators are stacked together to form a fuel cell stack of the power generation cells, e.g., mounted in a vehicle.

In the fuel cell, a fuel gas flow field (reactant gas flow field) for supplying a fuel gas is formed on a separator surface facing the anode, and an oxygen-containing gas flow field (reactant gas flow field) for supplying an oxygen-containing gas is formed on a separator surface facing the cathode.

Further, so-called internal manifold structure may be adopted in the fuel cell. In the structure, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage extend through the fuel cell for allowing an oxygen-containing gas to flow through the fuel cell in the stacking direction, and a fuel gas supply passage and a fuel gas discharge passage extend through the fuel cell for allowing a fuel gas to flow through the fuel cell in the stacking direction. Further, a coolant supply passage and a coolant discharge passage extend through the fuel cell for allowing a coolant to flow through the fuel cell in the stacking direction.

In the reactant gas flow fields, condensed water is produced, and water produced in the power generation is present. The water tends to be retained at the outlet of the reactant gas flow fields. In the structure, the reactant gas flow fields may be clogged by the retained water, and the fuel gas and the oxygen-containing gas may not be supplied to the anode and the cathode suitably.

In this regard, for example, a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2000-223137 includes a separator 1 as shown in FIG. 9. A fuel gas inlet 2 a, an air inlet 3 a, a coolant inlet 4 a are arranged diagonally with a fuel gas outlet 2 b, an air outlet 3 b, and a coolant outlet 4 b in the separator 1, and the inlets and the outlets extend through the separator 1.

An air channel 5 having a plurality of air flow grooves 5 a are formed on one surface of the separator 1 for allowing the air supplied from the air inlet 3 a to flow toward the air outlet 3 b. The air flow grooves 5 a of the air channel 5 flow in parallel, and form a serpentine flow field for allowing the air to flow left and right, and move downwardly.

The air flow grooves 5 a of the air channel 5 are configured such that the sectional area in the flow field is progressively reduced from the air inlet 3 a to the air outlet 3 b, i.e., toward the downstream side. According to the disclosure, reduction in the flow speed at the air outlet 3 b is suppressed, and the water is not retained easily on the air outlet 3 b side advantageously.

However, in Japanese Laid-Open Patent Publication No. 2000-223137, since the air flow grooves 5 a form the serpentine flow field, the flow grooves connecting the air inlet 3 a to the air outlet 3 b are significantly long. In the structure, the pressure loss in each of the air flow grooves 5 a is significantly large. In particular, it is required to keep the high outputs of devices such as a compressor and a supercharger for supplying the air to the air inlet 3 a. Therefore, the devices have large sizes uneconomically.

Further, in a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2006-032008, as shown in FIG. 10, a hydrogen side separator 1 c is provided. The separator 1 c is formed by a single metal plate 2 c. The separator 1 c has a corrugated power generation area 3 c formed by pressure forming.

A hydrogen gas flow field 4 c is formed on one surface of the separator 1 c, and a coolant water flow field is formed on the other surface of the separator 1 c. A hydrogen gas distribution channel 5 c for distributing a hydrogen gas to the hydrogen gas flow field 4 c is formed inside a rib 6 c formed integrally with the metal plate 2 c by resin molding. A hydrogen manifold hole 7 c, a coolant water manifold hole 8 c, and an air manifold hole 9 c extend through the separator 1 c in the stacking direction. The hydrogen manifold hole 7 c is connected to the hydrogen gas flow field 4 c through the hydrogen gas distribution channel 5 c.

However, in Japanese Laid-Open Patent Publication No. 2006-032008, the hydrogen cannot be distributed uniformly from the hydrogen manifold hole 7 c to the hydrogen gas flow field 4 c easily, and the hydrogen distribution performance is low. By designing flow grooves in the hydrogen gas distribution channel 5 c connecting the hydrogen manifold hole 7 c to the hydrogen gas flow field 4 c to be considerably long, the desired hydrogen distribution performance may be achieved. However, in the structure, the separator 1 itself has a large size in the flow direction of the hydrogen gas flow field 4 c, adversely.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problem, and an object of the present invention is to provide a fuel cell which makes it possible to reliably prevent water produced in a power generation reaction from being retained at the outlet of a reactant gas flow field, and ensure that the power generation reaction occurs desirably without any interruption.

Further, an object of the present invention is to provide a fuel cell in which improvement in the performance of distributing a fuel gas and an oxygen-containing gas is achieved without requiring any elongated separator, and the desired power generation performance is maintained.

The present invention relates to a fuel cell formed by stacking an electrolyte electrode assembly and a separator in a stacking direction. The electrolyte electrode assembly includes electrodes and an electrolyte interposed between the electrodes. A reactant gas supply passage and a reactant gas discharge passage extend through the fuel cell for allowing a reactant gas to flow in the stacking direction. A reactant gas flow field is formed between the electrolyte electrode assembly and the separator for allowing the reactant gas to flow along an electrode surface.

The reactant gas flow field includes an inlet channel having a plurality of flow grooves connected to the reactant gas supply passage, an outlet channel having a plurality of flow grooves connected to the reactant gas discharge passage, and an intermediate channel having a plurality of flow grooves with both ends connected to the inlet channel and the outlet channel respectively. The flow grooves of the outlet channel are longer than the flow grooves of the inlet channel.

Further, the present invention relates to a fuel cell formed by stacking an electrolyte electrode assembly and a separator in a stacking direction. The electrolyte electrode assembly includes a cathode, an anode, and an electrolyte interposed between the cathode and the anode, an oxygen-containing gas flow field for supplying an oxygen-containing gas along the cathode and a fuel gas flow field for supplying a fuel gas along the anode being formed in the fuel cell. An oxygen-containing gas supply passage and an oxygen-containing gas discharge passage for allowing the oxygen-containing gas to flow in the stacking direction, and a fuel gas supply passage and a fuel gas discharge passage for allowing the fuel gas to flow in the stacking direction are provided in the fuel cell.

The oxygen-containing gas discharge passage, and a pair of the fuel gas supply passages on both sides of the oxygen-containing gas discharge passage are provided at one end of the separator.

The fuel gas discharge passage, and a pair of the oxygen-containing gas supply passages on both sides of the fuel gas discharge passage are provided at the other end of the separator.

According to an aspect of the present invention, the flow grooves of the outlet channel connecting the intermediate channel and the reactant gas discharge passage are longer than the flow grooves of the inlet channel connecting the intermediate channel and the reactant gas supply passage. In the structure, in the outlet channel where the flow grooves are narrowed from the intermediate channel toward the reactant gas discharge passage, the flow grooves are relatively long, and the flow speed of the reactant gas is increased, and improvement in the performance of discharging the retained water which tends to be condensed over a wide area is achieved.

Accordingly, though the water produced in the power generation tends to be retained at the outlet of the reactant gas flow field, the water can be discharged easily and reliably into the reactant gas discharge passage. Thus, with the simple structure, the performance of discharging the water is improved, and it is possible to ensure that the power generation reaction occurs desirably without any interruptions.

Further, according to an aspect of the present invention, since a pair of fuel gas supply passages are provided at one end of the separator, the fuel gas can be distributed suitably, and the length of the flow grooves extending from the fuel gas supply passages to the fuel gas flow field is reduced effectively. Further, since a pair of oxygen-containing gas supply passages are provided at the other end of the separator, improvement in the performance of distributing the oxygen-containing gas is achieved, and the length of the flow grooves extending from the oxygen-containing gas supply passages to the oxygen-containing gas flow field is reduced effectively.

Accordingly, it is possible to improve the performance of distributing the fuel gas and the oxygen-containing gas without requiring any elongated separators.

Further, the fuel gas and the oxygen-containing gas flow in a counterflow manner over the entire electrode surfaces. In the structure, the humidity environment in the electrode surfaces is uniformized easily, and improvement in the power generation performance is achieved.

The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a fuel cell according to a first embodiment of the present invention;

FIG. 2 is a front view showing a cathode side separator of the fuel cell;

FIG. 3 is an exploded perspective view showing a fuel cell according to a second embodiment of the present invention;

FIG. 4 is a front view showing a cathode side separator of the fuel cell;

FIG. 5 is an exploded perspective view showing a fuel cell according to a third embodiment of the present invention;

FIG. 6 is a front view showing a cathode side separator of the fuel cell;

FIG. 7 is an exploded perspective view showing a fuel cell according to a fourth embodiment of the present invention;

FIG. 8 is a front view showing a cathode side separator of the fuel cell;

FIG. 9 is a view showing a separator of a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2000-223137; and

FIG. 10 is a view showing a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2006-032008.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a fuel cell 10 according to a first embodiment of the present invention includes a membrane electrode assembly (electrolyte electrode assembly) 12, and a cathode side separator 14 and an anode side separator 16 sandwiching the membrane electrode assembly 12. For example, the cathode side separator 14 and the anode side separator 16 are carbon separators. Alternatively, the cathode side separator 14 and the anode side separator 16 may be formed by corrugating metal separators.

At one end of the fuel cell 10 in a horizontal direction indicated by an arrow B, an oxygen-containing gas supply passage 18 a for supplying an oxygen-containing gas (reactant gas), a coolant supply passage 20 a for supplying a coolant, and a fuel gas discharge passage 22 b for discharging a fuel gas (reactant gas), e.g., a hydrogen-containing gas, are provided. The oxygen-containing gas supply passage 18 a, the coolant supply passage 20 a, and the fuel gas discharge passage 22 b extend through the fuel cell 10 in the direction indicated by an arrow A.

At the other end of the fuel cell 10 in the direction indicated by the arrow B, an oxygen-containing gas discharge passage 18 b for discharging the oxygen-containing gas, a coolant discharge passage 20 b for discharging the coolant, and a fuel gas supply passage 22 a for supplying the fuel gas are provided. The oxygen-containing gas discharge passage 18 b, the coolant discharge passage 20 b, and the fuel gas supply passage 22 a extend through the fuel cell 10 in the direction indicated by the arrow A.

As shown in FIGS. 1 and 2, the cathode side separator 14 has an oxygen-containing gas flow field 24 on a surface 14 a facing the membrane electrode assembly 12 for allowing the oxygen-containing gas to flow between the membrane electrode assembly 12 and the separator surface.

As shown in FIG. 2, the oxygen-containing gas flow field 24 includes an inlet channel 24 a having a plurality of flow grooves connected to the oxygen-containing gas supply passage 18 a and an outlet channel 24 b having a plurality of flow grooves connected to the oxygen-containing gas discharge passage 18 b, and an intermediate channel 24 c having a plurality of flow grooves with both ends connected to the inlet channel 24 a and the outlet channel 24 b respectively. The length L1 of the flow grooves of the inlet channel 24 a is smaller than the length L2 of the flow grooves of the outlet channel 24 b (L1<L2).

The inlet channel 24 a form a first narrowed portion where the flow grooves in the inlet channel 24 a are narrowed from the intermediate channel 24 c toward the oxygen-containing gas supply passage 18 a. The outlet channel 24 b forms a second narrowed portion where the flow grooves in the outlet channel 24 b are narrowed from the intermediate channel 24 c toward the oxygen-containing gas discharge passage 18 b. The flow grooves of the intermediate channel 24 c extend in the direction indicated by the arrow B in parallel to each other, and have the same length.

An inlet connection channel 26 a is formed between the oxygen-containing gas supply passage 18 a and the inlet channel 24 a. The inlet connection channel 26 a includes a plurality of flow grooves extending in parallel to each other. An outlet connection channel 26 b is formed between the oxygen-containing gas discharge passage 18 b and the outlet channel 24 b. The outlet connection channel 26 b has a plurality of flow grooves extending in parallel to each other.

As shown in FIG. 1, a coolant flow field 28 is formed on a surface 14 b, opposite to the surface 14 a of the cathode side separator 14. The coolant flow field 28 is connected to the coolant supply passage 20 a and the coolant discharge passage 20 b, and has a plurality of flow grooves 28 a extending in the direction indicated by the arrow B.

The anode side separator 16 has a fuel gas flow field 30 on a surface 16 a facing the membrane electrode assembly 12 for supplying the fuel gas between the membrane electrode assembly 12 and the separator surface.

The fuel gas flow field 30 includes an inlet channel 30 a having a plurality of flow grooves connected to the fuel gas supply passage 22 a, an outlet channel 30 b having a plurality of flow grooves connected to the fuel gas discharge passage 22 b, and an intermediate channel 30 c having a plurality of flow grooves with both ends connected to the inlet channel 30 a and the outlet channel 30 b respectively. The length L3 of the flow grooves of the inlet channel 30 a is smaller than the length L4 of the flow grooves of the outlet channel 30 b (L3<L4).

The inlet channel 30 a forms a first narrowed portion where the flow grooves of the inlet channel 30 a are narrowed from the intermediate channel 30 c toward the fuel gas supply passage 22 a. The outlet channel 30 b includes a second narrowed portion where the flow grooves of the outlet channel 30 b are narrowed from the intermediate channel 30 c toward the fuel gas discharge passage 22 b. The flow grooves of the intermediate channel 30 c extend in the direction indicated by the arrow B in parallel to each other, and have the same length.

An inlet connection channel 32 a is formed between the fuel gas supply passage 22 a and the inlet channel 30 a. The inlet connection channel 32 a includes a plurality of flow grooves extending in parallel to each other. An outlet connection channel 32 b is formed between the fuel gas discharge passage 22 b and the outlet channel 30 b. The outlet connection channel 32 b has a plurality of flow grooves extending in parallel to each other.

Though not shown, seal members are provided on the cathode side separator 14 and the anode side separator 16.

Each of the membrane electrode assemblies 12 includes a cathode 36, an anode 38, and a solid polymer electrolyte membrane (electrolyte) 34 interposed between the cathode 36 and the anode 38. The solid polymer electrolyte membrane 34 is formed by impregnating a thin membrane of perfluorosulfonic acid with water, for example. For example, the cathode 36 and the anode 38 have a hexagonal shape.

The cathode 36 has a gas diffusion layer of porous conductive material such as a carbon paper, and an electrode catalyst layer of platinum alloy supported on porous carbon particles. The carbon particles are deposited uniformly on the surface of the gas diffusion layer. The electrode catalyst layer of the cathode 36 is fixed to one surface of the solid polymer electrolyte membrane 34.

The anode 38 has a gas diffusion layer of porous conductive material such as a carbon paper, and an electrode catalyst layer of platinum alloy supported on porous carbon particles. The carbon particles are deposited uniformly on the surface of the gas diffusion layer. The electrode catalyst layer of the anode 38 is fixed to the other surface of the solid polymer electrolyte membrane 34.

Operation of the fuel cell 10 will be described below. As shown in FIG. 1, an oxygen-containing gas such as the air is supplied to the oxygen-containing gas supply passage 18 a, and a fuel gas such as a hydrogen gas is supplied to the fuel gas supply passage 22 a.

The oxygen-containing gas flows from the oxygen-containing gas supply passage 18 a into the oxygen-containing gas flow field 24 formed on the surface 14 a of the cathode side separator 14. Thus, the oxygen-containing moves along the oxygen-containing gas flow field 24, and the oxygen-containing gas is supplied to the cathode 36 of the membrane electrode assembly 12 for inducing an electrochemical reaction at the cathode 36.

The fuel gas flows from the fuel gas supply passage 22 a into the fuel gas flow field 30 of the anode side separator 16. The fuel gas moves along the fuel gas flow field 30, and the fuel gas is supplied to the anode 38 of the membrane electrode assembly 12 for inducing an electrochemical reaction at the anode 38.

Thus, in the membrane electrode assembly 12, the oxygen-containing gas supplied to the cathode 36 and the fuel gas supplied to the anode 38 are consumed in the electrochemical reactions at electrode catalyst layers of the cathode 36 and the anode 38 for generating electricity.

Then, the oxygen-containing gas consumed at the cathode 36 is discharged into the oxygen-containing gas discharge passage 18 b. The fuel gas consumed at the anode 38 is discharged into the fuel gas discharge passage 22 b.

Further, a coolant such as pure water, ethylene glycol, oil or the like is supplied to the coolant supply passage 20 a. The coolant flows along the coolant flow field 28 formed between the anode side separator 16 and the cathode side separator 14. After the coolant cools the membrane electrode assembly 12, the coolant is discharged into the coolant discharge passage 20 b.

In the first embodiment, as shown in FIG. 2, the oxygen-containing gas flow field 24 provided in the cathode side separator 14 has the inlet channel 24 a forming the first narrowed portion, the outlet channel 24 b forming the second narrowed portion, and the intermediate channel 24 c including the parallel flow grooves. The length L2 of the flow grooves of the outlet channel 24 b is larger than the length L1 of the flow grooves of the inlet channel 24 a.

In the structure, the outlet channel 24 b is narrowed from the intermediate channel 24 c toward the oxygen-containing gas discharge passage 18 b to have a flow speed gradient, i.e., to have the capability of increasing the flow speed of the oxygen-containing gas, and the outlet channel 24 b is relatively elongated. Therefore, the flow speed of the oxygen-containing gas flowing through the outlet channel 24 b is increased. Thus, though the water produced in the fuel cell 10 tends to condense over a wide area at the outlet of the oxygen-containing gas flow field 24, the water is discharged smoothly.

Accordingly, the produced water which tends to be retained at the outlet of the oxygen-containing gas flow field 24 can be discharged into the oxygen-containing gas discharge passage 18 b easily and reliably. With the simple structure, improvement in the performance of discharging the water is achieved, and the power generation reaction occurs desirably without any interruption.

Further, in the first embodiment, the oxygen-containing gas in the oxygen-containing gas flow field 24 and the fuel gas in the fuel gas flow field 30 flow in a counterflow manner. The oxygen-containing gas in the oxygen-containing gas flow field 24 and the coolant in the coolant flow field 28 flow in parallel to each other. In the structure, it is possible to achieve a uniform humidity distribution on the power generation surfaces of the membrane electrode assembly 12, and improvement in the power generation performance is achieved easily.

Further, the oxygen-containing gas, the fuel gas, and the coolant do not flow in serpentine patterns, but flow straight. In the structure, it is possible to achieve a uniform distribution on the power generation surfaces of the membrane electrode assembly 12, and improvement in the power generation performance is achieved easily.

FIG. 3 is an exploded perspective view showing a fuel cell 40 according to a second embodiment of the present invention.

The constituent elements that are identical to those of the fuel cell 10 according to the first embodiment are labeled with the same reference numerals, and detailed descriptions thereof will be omitted. Further, in third and fourth embodiments as described later, the constituent elements that are identical to those of the fuel cell 10 according to the first embodiment are labeled with the same reference numerals, and detailed descriptions thereof will be omitted.

The fuel cell 40 includes a membrane electrode assembly 42, and a cathode side separator 44 and an anode side separator 46 sandwiching the membrane electrode assembly 42. The cathode side separator 44 and the anode side separator 46 are metal separators. Alternatively, carbon separators may be used as the cathode side separator 44 and the anode side separator 46.

At one end of the fuel cell 40 in a direction indicated by an arrow B, a pair of oxygen-containing gas supply passages 18 a 1, 18 a 2 at upper and lower positions, a pair of coolant supply passages 20 a 1, 20 a 2 between the oxygen-containing gas supply passages 18 a 1, 18 a 2, and a single fuel gas discharge passage 22 b between the coolant supply passages 20 a 1, 20 a 2 are provided.

At the other end of the fuel cell 40 in the direction indicated by the arrow B, a pair of fuel gas supply passages 22 a 1, 22 a 2 at upper and lower positions, a pair of coolant discharge passages 20 b 1, 20 b 2 between the fuel gas supply passages 22 a 1, 22 a 2, and a single oxygen-containing gas discharge passage 18 b between the coolant discharge passages 20 b 1, 20 b 2 are provided.

As shown in FIG. 4, an oxygen-containing gas flow field 24 is formed on a surface 14 a of the cathode side separator 44. The oxygen-containing gas flow field 24 includes inlet channels 24 a 1, 24 a 2 each having a plurality of flow grooves connected to the oxygen-containing gas supply passages 18 a 1, 18 a 2, respectively, outlet channels 24 b 1, 24 b 2 each having a plurality of flow grooves connected to the oxygen-containing gas discharge passage 18 b, an intermediate channel 24 c 1 having a plurality of flow grooves with both ends connected to the inlet channel 24 a 1 and the outlet channel 24 b 1 respectively, and an intermediate channel 24 c 2 each having a plurality of flow grooves with both ends connected to the inlet channel 24 a 2 and the outlet channel 24 b 2 respectively.

The inlet channels 24 a 1, 24 a 2 form a first narrowed portion. Each of the flow grooves in the inlet channels 24 a 1, 24 a 2 extends from the oxygen-containing gas supply passages 18 a 1, 18 a 2 to the intermediate channels 24 c 1, 24 c 2 and is divided into two flow grooves in midstream. Then, the flow grooves in the inlet channels 24 a 1, 24 a 2 are curved horizontally, and connected to the respective intermediate channels 24 c 1, 24 c 2.

The outlet channels 24 b 1, 24 b 2 are connected to the intermediate channels 24 c 1, 24 c 2. The direction of the flow grooves is changed toward a central line O1. The outlet channels 24 b 1, 24 b 2 have a portion where two flow grooves are merged into one flow groove, and a portion where three flow grooves are merged into two flow grooves, and then merged into one flow groove.

Inlet connection channels 26 a 1, 26 a 2 each having a plurality of flow grooves extending in parallel to each other are provided between the oxygen-containing gas supply passages 18 a 1, 18 a 2 and the inlet channels 24 a 1, 24 a 2. Outlet connection channels 26 b 1, 26 b 2 each having a plurality of flow grooves extending in parallel to each other are provided between the oxygen-containing gas discharge passage 18 b and the outlet channels 24 b 1, 24 b 2.

The cathode side separator 44 has a vertically symmetrical shape with respect to the central line 01 extending in the direction indicated by the arrow B, at the center in a direction indicated by an arrow C (see FIG. 4).

As shown in FIG. 3, a fuel gas flow field 30 is formed on a surface 16 a of the anode side separator 46. The fuel gas flow field 30 includes inlet channels 30 a 1, 30 a 2 each having a plurality of flow grooves connected to the fuel gas supply passages 22 a 1, 22 a 2, outlet channels 30 b 1, 30 b 2 each having a plurality of flow grooves connected to the single fuel gas discharge passage 22 b, an intermediate channel 30 c 1 having a plurality of flow grooves with both ends connected to the inlet channel 30 a 1 and the outlet channel 30 b 1 respectively, and an intermediate channel 30 c 2 having a plurality of flow grooves with both ends connected to the inlet channel 30 a 2 and the outlet channel 30 b 2 respectively.

The length of the flow grooves of the outlet channels 30 b 1, 30 b 2 is longer than the length of the flow grooves of the inlet channels 30 a 1, 30 a 2. The number of flow grooves in the inlet channels 30 a 1, 30 a 2 is increased toward the intermediate channels 30 c 1, 30 c 2. The outlet channels 30 b 1, 30 b 2 have portions where the number of flow grooves is decreased from two to one from the intermediate channels 30 c 1, 30 c 2 toward the fuel gas discharge passage 22 b, and portions where the number of flow grooves is decreased from three to two, and then two to one from the intermediate channels 30 c 1, 30 c 2 toward the fuel gas discharge passage 22 b.

Inlet connection channels 32 a 1, 32 a 2 are provided between the fuel gas supply passages 22 a 1, 22 a 2 and the inlet channels 30 a 1, 30 a 2. Outlet connection channels 32 b 1, 32 b 2 are provided between the fuel gas discharge passage 22 b and the outlet channels 30 b 1, 30 b 2.

The anode side separator 46 has a vertically symmetrical shape with respect to the central line O2 extending in the direction indicated by the arrow B, at the center in a direction indicated by the arrow C.

A surface 14 b of the cathode side separator 44 and a surface 16 b of the anode side separator 46 are overlapped with each other, and the coolant flow field 28 is formed between the back surface of the oxygen-containing gas flow field 24 and the back surface of the fuel gas flow field 30.

In the second embodiment, the same advantages as in the case of the first embodiment are obtained.

Further, as shown in FIG. 4, the outlet channels 24 b 1, 24 b 2 of the oxygen-containing gas flow field 24 include portions where the number of flow grooves is reduced from two to one, and portions where the number of flow grooves is reduced from three to two, and then, two to one. In the structure, the flow rate adjustment can be made without adding a pressure loss element such as the narrowed portion. In particular, it is possible to eliminate the retained water droplets as much as possible.

FIG. 5 is an exploded perspective view showing a fuel cell 50 according to a third embodiment of the present invention.

The fuel cell 50 includes a membrane electrode assembly 52, and a cathode side separator 54 and an anode side separator 56 sandwiching the membrane electrode assembly 52. For example, the cathode side separator 54 and the anode side separator 56 are formed by corrugating metal separators. Alternatively, carbon separators may be used as the cathode side separator 54 and the anode side separator 56.

At one end of the fuel cell 50 in a horizontal direction indicated by an arrow B, a pair of oxygen-containing gas supply passages 18 a 1, 18 a 2 at upper and lower positions, a pair of coolant supply passages 20 a 1, 20 a 2 at upper and lower positions between the oxygen-containing gas supply passages 18 a 1, 18 a 2, and a single fuel gas discharge passage 22 b between the coolant supply passages 20 a 1, 20 a 2 are provided. The oxygen-containing gas supply passages 18 a 1, 18 a 2, the coolant supply passages 20 a 1, 20 a 2, and the fuel gas discharge passage 22 b extend through the fuel cell 50 in the direction indicated by an arrow A.

At the other end of the fuel cell 50 in the horizontal direction indicated by the arrow B, a pair of fuel gas supply passages 22 a 1, 22 a 2 at upper and lower positions, a pair of coolant discharge passages 20 b 1, 20 b 2 at upper and lower positions between the fuel gas supply passages 22 a 1, 22 a 2, and a single oxygen-containing gas discharge passage 18 b between the coolant discharge passages 20 b 1, 20 b 2 are provided. The fuel gas supply passages 22 a 1, 22 a 2, the coolant discharge passages 20 b 1, 20 b 2, and the oxygen-containing gas discharge passage 18 b extend through the fuel cell 50 in the direction indicated by the arrow A.

As shown in FIG. 6, an inlet buffer 57 a and an outlet buffer 57 b are provided on a surface 54 a of the cathode side separator 54. The inlet buffer 57 a is connected to the oxygen-containing gas supply passages 18 a 1, 18 a 2 through inlet connection channels 26 a 1, 26 a 2. The outlet buffer 57 b is connected to the oxygen-containing gas discharge passage 18 b through the outlet connection channel 26 b. The oxygen-containing gas flow field 24 has a plurality of flow grooves 24 d with both ends connected to the inlet buffer 57 a and the outlet buffer 57 b respectively, and extending in the direction indicated by the arrow B.

The total dimension (h1+h2) of the width h1 where the oxygen-containing gas flows into the inlet connection channel 26 a 1 connected to the oxygen-containing gas supply passage 18 a 1 and the width h2 where the oxygen-containing gas flows into the inlet connection channel 26 a 2 connected to the oxygen-containing gas supply passage 18 a 1 is larger than the width h3 where the oxygen-containing gas is discharged through the outlet connection channel 26 b connected to the oxygen-containing gas discharge passage 18 b (h1+h2>h3).

As shown in FIG. 5, the coolant flow field 28 is formed on the surface 54 b, opposite to the surface 54 a of the cathode side separator 54. Further, an inlet buffer 58 a and an outlet buffer 58 b are formed on the surface 54 b. The inlet buffer 58 a is connected to the coolant supply passages 20 a 1, 20 a 2, and the outlet buffer 58 b is connected to the coolant discharge passages 20 b 1, 20 b 2. The coolant flow field 28 has a plurality of flow grooves 28 b extending in the direction indicated by the arrow B. The flow grooves 28 b are formed on the back surface of the flow grooves 24 d.

An inlet buffer 60 a and an outlet buffer 60 b are formed on a surface 56 a of the anode side separator 56. The inlet buffer 60 a is connected to the fuel gas supply passages 22 a 1, 22 a 2 through inlet connection channels 32 a 1, 32 a 2, and the outlet buffer 60 b is connected to the fuel gas discharge passage 22 b through the outlet connection channel 32 b. The fuel gas flow field 30 has a plurality of flow grooves 30 d with both ends connected to the inlet buffer 60 a and the outlet buffer 60 b respectively, and extending in the direction indicated by the arrow B.

The total dimension (h4+h5) of the width h4 where the fuel gas flows into the inlet connection channel 32 a 1 connected to the fuel gas supply passage 22 a 1 and the width h5 where the fuel gas flows into the inlet connection channel 32 a 2 connected to the fuel gas supply passage 22 a 2 is larger than the width h6 where the fuel gas is discharged through the outlet connection channel 32 b connected to the fuel gas discharge passage 22 b (h4+h5>h6).

Seal members 59 a, 59 b are formed integrally with the cathode side separator 54 and the anode side separator 56.

Operation of the fuel cell 50 will be described below.

As shown in FIG. 5, an oxygen-containing gas such as the air is supplied to the oxygen-containing gas supply passages 18 a 1, 18 a 2, and a fuel gas such as a hydrogen gas is supplied to the fuel gas supply passage 22 a 1, 22 a 2.

The oxygen-containing gas from the oxygen-containing gas supply passages 18 a 1, 18 a 2 flow into the oxygen-containing gas flow field 24 through the inlet buffer 57 a formed on the surface 54 a of the cathode side separator 54. Thus, the oxygen-containing gas moves along the oxygen-containing gas flow field 24, and the oxygen-containing gas is supplied to the cathode 36 of the membrane electrode assembly 52 for inducing an electrochemical reaction at the cathode 36.

The fuel gas from the fuel gas supply passages 22 a 1, 22 a 2 flows into the fuel gas flow field 30 through the inlet buffer 60 a of the anode side separator 56. Thus, the fuel gas moves along the fuel gas flow field 30, and the fuel gas is supplied to the anode 38 of the membrane electrode assembly 52 for inducing an electrochemical reaction at the anode 38.

Thus, in the membrane electrode assembly 52, the oxygen-containing gas supplied to the cathode 36 and the fuel gas supplied to the anode 38 are consumed in the electrochemical reactions at electrode catalyst layers of the cathode 36 and the anode 38 for generating electricity.

The oxygen-containing gas consumed at the cathode 36 is discharged into the oxygen-containing gas discharge passage 18 b through the outlet buffer 57 b, and the fuel gas supplied to the anode 38 is discharged into the fuel gas discharge passage 22 b through the outlet buffer 60 b.

The coolant supplied to the coolant supply passages 20 a 1, 20 a 2 moves along the coolant flow field 28 formed between the anode side separator 56 and the cathode side separator 54. After the coolant cools the membrane electrode assembly 12, the coolant is discharged into the coolant discharge passages 20 b 1, 20 b 2.

In the third embodiment, a pair of the fuel gas supply passages 22 a 1, 22 a 2 are formed at one end of the cathode side separator 54 and the anode side separator 56. In the structure, improvement in the performance of distributing the fuel gas is achieved, and the length of the inlet buffer 60 a (distribution channel) from the fuel gas supply passages 22 a 1, 22 a 2 to the fuel gas flow field 30 is shortened effectively.

Likewise, a pair of the oxygen-containing gas supply passages 18 a 1, 18 a 2 are formed at the other end of the cathode side separator 54 and the anode side separator 56. In the structure, improvement in the performance of distributing the oxygen-containing gas is achieved, and the length of the inlet buffer 57 a (distribution channel) from the oxygen-containing gas supply passages 18 a 1, 18 a 2 to the oxygen-containing gas flow field 24 is shortened effectively.

Therefore, the cathode side separator 54 and the anode side separator 56 are prevented from being elongated in the direction indicated by the arrow B, and thus, reduction in the overall size of the fuel cell 50 is achieved easily. Further, improvement in the performance of distributing the fuel gas and the oxygen-containing gas is achieved suitably.

Moreover, the fuel gas in the fuel gas flow field 30 and the oxygen-containing gas in the oxygen-containing gas flow field 24 flow in a counterflow manner over the entire electrode surfaces of the membrane electrode assembly 52 (see FIG. 5). Further, the oxygen-containing gas flows in parallel with the coolant flowing through the coolant flow field 28. In the structure, it is possible to achieve a uniform humidity distribution on the power generation surfaces of the membrane electrode assembly 52, and improvement in the power generation performance is achieved easily.

Further, the total dimension of the width h1 where the oxygen-containing gas flows into the inlet connection channel 26 a 1 connected to the oxygen-containing gas supply passage 18 a 1 and the width h2 where the oxygen-containing gas flows into the inlet connection channel 26 a 2 connected to the oxygen-containing as supply passage 18 a 1 is larger than the width h3 where the oxygen-containing gas is discharged through the outlet connection channel 26 b connected to the oxygen-containing gas discharge passage 18 b (see FIG. 6). Therefore, the flow speed of the oxygen-containing gas is increased at the oxygen-containing gas discharge passage 18 b where the water produced in the power generation reaction tends to be condensed, and the condensed water can be discharged into the oxygen-containing gas discharge passage 18 b easily.

The total dimension of the width h4 where the fuel gas flows into the inlet connection channel 32 a 1 connected to the fuel gas supply passage 22 a 1 and the width h5 where the fuel gas flows into the inlet connection channel 32 a 2 connected to the fuel gas supply passage 22 a 2 is larger than the width h6 where the fuel gas is discharged through the outlet connection channel 32 b connected to the fuel gas discharge passage 22 b. In the structure, the condensed water is discharged to the fuel gas discharge passage 22 b suitably, and the desired power generation performance of the fuel cell 10 is achieved.

In the case where metal separators are used as the cathode side separator 54 and the anode side separator 56, the coolant flow field 28 is formed on the back surfaces of the fuel gas flow field 30 and the oxygen-containing gas flow field 24. In the structure, the shape of the coolant flow field 28 is simplified, and the coolant can be supplied into the coolant flow field 28 easily and reliably.

FIG. 7 is an exploded perspective view showing a fuel cell 60 according to a fourth embodiment of the present invention. The constituent elements that are identical to those of the fuel cell 40 according to the second embodiment are labeled with the same reference numerals, and detailed descriptions thereof will be omitted.

The fuel cell 60 includes a membrane electrode assembly 62, and a cathode side separator 64 and an anode side separator 66 sandwiching the membrane electrode assembly 62. The cathode side separator 64 and the anode side separator 66 are metal separators. Alternatively, the carbon separators may be used as the cathode side separator 64 and the anode side separator 66.

As shown in FIG. 8, the oxygen-containing gas supply passages 18 a 1, 18 a 2 are inclined from main flow fields 24 c 1, 24 c 2. Specifically, end surfaces 68 a 1, 68 a 2 at the oxygen-containing gas inlet, of the oxygen-containing gas supply passages 18 a 1, 18 a 2 are substantially perpendicular to the flow direction of the oxygen-containing gas in the inlet channels 24 a 1, 24 a 1. That is, the flow grooves of the inlet channels 24 a 1, 24 a 2 have substantially the same length from the oxygen-containing gas supply passages 18 a 1, 18 a 2 to ends of the main flow fields 24 c 1, 24 c 2.

End surfaces 68 b 1, 68 b 2 at the oxygen-containing gas outlet, of the oxygen-containing gas discharge passage 18 b are substantially perpendicular to the flow direction of the oxygen-containing gas in the outlet channels 24 b 1, 24 b 2. That is, the flow grooves of the outlet channels 24 b 1, 24 b 2 have substantially the same length from ends of the main flow fields 24 c 1, 24 c 2 to the oxygen-containing gas discharge passage 18 b.

As shown in FIG. 7, the end surfaces 70 a 1, 70 a 2 at the fuel gas inlet, of the fuel gas supply passages 22 a 1, 22 a 2 are substantially perpendicular to the flow direction of the fuel gas in the inlet channels 30 a 1, 30 a 2. That is, the flow grooves of the inlet channels 30 a 1, 30 a 2 have substantially the same length from the fuel gas supply passages 22 a 1, 22 a 2 to ends of the main flow fields 30 c 1, 30 c 2.

The end surfaces 70 b 1, 70 b 2 at the fuel gas outlet, of the fuel gas discharge passage 22 b are substantially perpendicular to the flow direction of fuel gas in the outlet channels 30 b 1, 30 b 2. That is, the flow grooves of the outlet channels 30 b 1, 30 b 2 have substantially the same length from ends of the main flow fields 30 c 1, 30 c 2 to the fuel gas discharge passage 22 b.

In the fourth embodiment, as shown in FIG. 8, the oxygen-containing gas supply passages 18 a 1, 18 a 2 are inclined from the main flow fields 24 c 1, 24 c 2. The oxygen-containing gas discharge passage 18 b is inclined from the main flow fields 24 c 1, 24 c 2.

In the structure, the flow grooves of the inlet channels 24 a 1, 24 a 2 have the same length, and the flow grooves in the outlet channels 24 b 1, 24 b have the same length. Therefore, variation in the flow groove length is suppressed in the entire oxygen-containing gas flow field 24. Accordingly, the oxygen-containing gas is distributed uniformly over the entire oxygen-containing gas flow field 24.

Likewise, variation in the flow groove length is suppressed in the entire fuel gas flow field 30. Accordingly, the fuel gas is distributed uniformly over the entire fuel gas flow field 30, and thus good electric generation performance can be achieved. Moreover, the same advantages as in the case of the third embodiment are obtained.

While the invention has been particularly shown and described with reference to the preferred embodiments, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the spirit of the invention as defined by the appended claims. 

What is claimed is:
 1. A fuel cell formed by stacking an electrolyte electrode assembly and a separator in a stacking direction, the eleCttolyte electrode assembly including a cathOde, an anode, and, an electrolyte interposed between the cathode and the anode, an oxygen-containing gas flow field for supplying an oxygen-containing gas along the cathode only in one direction and a fuel gas flow field for supplying a fuel gas along the anode only in another direction opposite to the one direction being formed in the fuel cell, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage for allowing the oxygen-containing gas to flow in the stacking direction, and a fuel gas supply passage and a fuel gas discharge passage for allowing the fuel gas to flow in the stacking direction being provided in the fuel cell, wherein the oxygen-containing gas discharge passage, and a pair of the fuel gas supply passages on both sides of the oxygen-containing gas discharge passage are provided at one end and on a surface of the separator; and the fuel gas discharge passage, and a pair of the oxygen-containing gas supply passages on both sides of the fuel gas discharge passage are provided at another end and on the surface of the separator.
 2. A fuel cell according to claim 1, wherein each one of a pair of coolant discharge passages is provided between the oxygen-containing gas discharge passage and each one of the pair of the fuel gas supply passages at the one end and on the surface of the separator; and each one of a pair of coolant supply passages is provided between the fuel gas discharge passage and each one of the pair of the oxygen-containing gas supply passages at the other end and on the surface of the separator.
 3. A fuel cell according to claim 1, wherein at least, the total dimension of the widths of the pair of the oxygen containing gas supply passages where the oxygen-containing gas flows from the oxygen-containing gas supply passages is larger than the width where the oxygen-containing gas is discharged into the oxygen-containing gas discharge passage, or the total dimension of the widths of the pair of the fuel gas supply passages where the fuel gas flows from the fuel gas supply passages is larger than the width where the fuel gas is discharged into the fuel gas discharge passage.
 4. A fuel cell according to claim 1, wherein the separator has a rectangular shape symmetrical with respect to a central line extending parallel to a short side through a center of a long side.
 5. A fuel cell according to claim 1, wherein at least, the oxygen-containing gas supply passage and, the oxygen-containing gas discharge passage are inclined from a main flow field of the oxygen-containing gas flow field, or the fuel gas supply passage and the fuel gas discharge passage are inclined from a main flow field of the fuel gas flow field.
 6. A fuel cell formed by stacking an electrolyte electrode assembly and a rectangular separator in a stacking direction, the electrolyte electrode assembly including a cathode, an anode, and an electrolyte interposed between the cathode and the anode, an oxygen-containing gas flow field for supplying an oxygen-containing gas along the cathode only in a same direction and a fuel gas flow field for supplying a fuel gas along the anode only in a same direction being formed in the fuel cell, oxygen-containing gas passages for allowing the oxygen-containing gas to flow in the stacking direction, and fuel gas passages for allowing the fuel gas to flow in the stacking direction being provided in the fuel cell, wherein one of the oxygen-containing gas passages and a pair of the fuel gas supply passages provided on both sides of the oxygen-containing gas passage are arranged at an end of one short side and on a surface of the separator; one of the fuel gas passages, and a pair of the oxygen-containing gas supply passages provided on both sides of the fuel, gas discharge passage are arranged at an end of another short side and on the surface of the separator; and the oxygen-containing gas passages include an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage, and the fuel gas passages include a fuel gas supply passage and a fuel gas discharge passage.
 7. A fuel cell according to claim 6, wherein the oxygen-containing gas flow field allows the oxygen-containing gas to flow on the surface of the separator in one direction, and the fuel gas flow field allows the fuel gas to flow in another direction opposite to the one direction.
 8. A fuel cell according to claim 6, wherein the separator has a shape symmetrical with respect to a central line extending parallel to the short sides through a center of a long side. 